Frost Formation Around A Vertical Cylinder In A Wet Air Stream

This paper describes a two dimensional model which permits evaluating the local thermal and geometrical properties during the process of frost formation. To achieve this objective it is necessary to know the local heat and mass transfer coefficients and hence solve the flow, heat and humidity fields. The solution is based upon converting the field functions in terms of the vorticity and stream functions. Once the heat and mass transfer coefficients are determined, a two stage model of the frost formation is used to determine the growth rate of frost layer. The numerical predictions were compared with existing numerical and experimental results and good agreement is found. Other results demonstrate the variation of frost density, frost thickness and the temperature field are presented and discussed.17213514

Investigating thermo-hydraulic behavior of pillow plate heat exchangers using entropy generation approach

Pillow plate heat exchanger (PPHE) is a modern type of plate heat exchanger composed of wavy shape parallel plates. Adjustment of the geometrical parameters has been broadly made to enhance the heat transfer performance of PPHEs. However, there has been limited attention to the thermo-hydraulic features and entropy generation of fluid flow through such heat exchangers. Addressing this gap could help further understanding of such heat exchangers. In the present study, Ansys CFX is used to simulate turbulent flow and heat transfer in inner pillow plate channels. The local entropy generation due to thermal effects and friction is calculated as a post processed task. The influence of the channel height, Prandtl number, diameter and arrangement of spot welds on the overall entropy generation of pillow plates are analyzed. The results indicate that by increasing the channel height, thermal entropy generation increases. Besides, increasing the spot weld diameter leads to a higher frictional loss in pillow plate channels, while the effect of spot weld size on thermal entropy generation is negligible. Also, the spot weld arrangement significantly affects the thermal and hydraulic characteristics of PPHEs. The results show that exergy analysis can be considered as a potential tool for investigating thermo-hydraulic behavior of PPHEs.</p

Experimental correlations for the solidification and fusion times of PCM encapsulated in spherical shells

This paper reports the results of a study to investigate and develop correlations for the parameters affecting the time for complete solidification and fusion in spherical shells. For this study, four spherical shells of 35, 76, 106 and 131 mm diameter were used, the charging temperature was varied from -20 degrees C to -5 degrees C while the melting temperature varied from 10 degrees C to 25 degrees C. Water and mixtures of water and polyethylene glycol in percentages ranging from 7.5% to 50% were tested. The developed correlation for the time for complete solidification showed an agreement with experiments with maximum difference of about 5.91%. Validation of the correlation of the time for complete fusion showed maximum difference of 7.2% and minimum difference of 0.88% when compared with experimental resultsCONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQ304372/2016-

Climate impact on combined cycle thermoelectric power plant in hot and humid regions

Thermoelectric power plants have been designed to operate in ISO conditions, similar to the temperate climatic conditions of the northern hemisphere. Thus, some equipment used in tropical regions operated outside the ideal conditions, with high relative humidity and ambient temperature. This ends up impairing its efficiency and maximum generation. This paper presents the analysis of 2020 and 2021 hourly electric generation and climatic conditions data for 2020 from the gas based combined cycle Cuiabá Thermoelectric Power Plant, located in the state of Mato Grosso do Sul, center-west region of Brazil. The main objective is to present and discuss the correlations between meteorological conditions and power generation in the plant. Results show a strong correlation between generation and the wet bulb temperature. They also show that high wind speeds, increase thermal losses and the efficiency of the steam cycle. This paper shows that thermal electric power plants are particularly sensitive to climate conditions in hot and humid regions